1. Field of the Invention
The present invention relates to a switching system, and more particularly to a magnetic proximity switch system.
2. Discussion of the Related Art
Conventional high security switches are based on reed switch technology which are shown in U.S. Pat. No. 4,339,747 (Maybee); U.S. Pat. No. 5,057,807 (Longly et al.); U.S. Pat. No. 5,128,641 (Posey); U.S. Pat. No. 5,233,322 (Posey); U.S. Pat. No. 5,293,523 (Posey); and U.S. Pat. No. 3,305,805 (Tann), which are hereby incorporated by reference. Also, examples of high security switches include U.S. Pat. No. 2,912,540 (Sawicki); U.S. Pat. No. 3,974,469 (Nicholls); U.S. Pat. No. 4,210,888 (Holce); U.S. Pat. No. 4,213,110 (Holce); U.S. Pat. No. 4,544,903 (Grant); U.S. Pat. No. 4,945,340 (Brill); and U.S. Pat. No. 5,233,323 (Burkett et al.) which are hereby incorporated by reference.
Reed switch systems generally comprise a single reed switch that is actuated into the electrically closed position when in proximity of an actuator that includes a permanent magnet. The reed switch is usually mounted in or about the frame surrounding a doorway, window, or access panel while the actuator is usually mounted to the movable member such as a door or a window. However, reed switch systems represent a trivial obstacle to any intruder. For example, if access to the reed switch system is gained, a single permanent magnet can mimic the actuator to actuate the reed switch. Even if access cannot be gained, the reed switch can be actuated by a very powerful permanent magnet from the outside.
Conventional high security switches attempt to overcome this problem. High security switch systems typically consist of a fixed switch assembly and a movable actuator assembly wherein the switch assembly comprises some combination of two or more directionally biased reed switches. The directional biasing is achieved by using a small external magnet to induce a magnetic orientation of a leaf spring in a reed switch. Here, the switches are configured to have different directionalities. Accordingly, the actuator assembly comprises some combination of two or more permanent magnets corresponding to the directionality of the switches. The purpose of the multiple reed switch combination is to make the switch assembly difficult to defeat with a single permanent magnet. Ideally, a high security switch should be immune to defeat by another actuator of the same type or specifically designed lock picking magnet assemblies. However, conventional high security switches can be defeated.
For example, the directionality of all the switches can be re-oriented in the same direction by using a larger magnet since the directionality is achieved by induction. The switch assembly can then be actuated by a single magnet. Also, the switches can be actuated by placing a second actuator of the same type on the side of the switch assembly. Accordingly, all of the conventional technology is susceptible to defeat by single permanent magnets, another actuator, or some lock picking mechanism.
Furthermore, the biasing technique is further limited because of the small size of the components, variations in magnetic and mechanical properties, and complications from hysteresis. Moreover, adjustment in the biasing is difficult because magnetic behavior is nonlinear. Furthermore, the operation of the reed switches are interfered by magnetic fields from adjacent switches, thereby causing system failures.
Because conventional reed switch technology suffers from the above-noted limitations and disadvantages, an alternative design is needed.